A Comparative Study for Estimating Crop Evapotranspiration in the Sacramento-San Joaquin Delta
Josué Medellín-Azuara, Kyaw Tha Paw U, Yufang Jin, and Jay R. Lund
Project Contact: Josue Medellin-Azuara or Jesse Jankowski (Delta CU Main Report) Kyaw Tha Paw U (Field Campaign Delta CU Study)
(Full list of authors and contributors below)
This research project was convened by the Center for Watershed Sciences at the University of California Davis with financial support from the California State Water Resources Control Board Office of the Delta Watermaster and other agencies. Its objective is to develop a better understanding of consumptive water use in the Delta by coordinating modeling, measurement, and other information from a variety of independent research and estimation efforts.
Consumptive water use by crops, often referred to as evapotranspiration (ET), is frequently the largest component of an agricultural region’s water balance. This study investigates crop consumptive use in the Sacramento-San Joaquin Delta (“Delta”) of California using a comparative approach with several prominent methods for estimating crop ET, including estimates based on crop coefficients, water balances, energy balance using remote sensing, and field measurements.
Crop ET estimates are provided for both the Legal Delta and the Delta Service Area (DSA) for two water years (2015 and 2016) by seven methods:
- CalSIMETAW: California Simulation of Evapotranspiration of Applied Water, by the California Department of Water Resources (DWR).
- DETAW: Delta Evapotranspiration of Applied Water, by DWR.
- DisALEXI: Disaggregated Atmosphere-Land Exchange Inverse method, by the U.S. Department of Agriculture Agricultural Research Service (USDA-ARS).
- ITRC-METRIC: Mapping Evapotranspiration at High Resolution with Internalized Calibration (METRIC), by the Irrigation Training and Research Center (ITRC) at California Polytechnic State University (Cal Poly).
- SIMS: Satellite Irrigation Management Support System, by the National Aeronautics and Space Administration Ames Research Center (NASA-ARC) and California State University Monterey Bay (CSUMB).
- UCD-METRIC: Mapping Evapotranspiration at High Resolution with Internalized Calibration (METRIC), by the University of California (UC) Davis.
- UCD-PT: Optimized Priestley-Taylor approach, by UC Davis.
In addition, field-based estimates and measurements of ET using eddy covariance and estimates with surface renewal stations were developed over bare soil during the fall of 2015 and over three predominant crops in the Delta (alfalfa, corn, and pasture) in the 2016 irrigation season. One direct ET measurement station was also deployed in 2016. Five additional California Irrigation Management Information System (CIMIS) stations were deployed in the Delta in 2016 to improve the spatial representation of weather variables and accuracy in input datasets of reference ET estimates. Two annual land use parcel surveys for 2015 and 2016 were conducted by Land IQ, Inc., which provided updated land use maps over the study area with more than 30 land use classes. A total of 26 agricultural classes were used for ET estimates and analysis.
Additional Funding and Research Support from
California State Water Resources Control Board, California Department of Water Resources, Delta Protection Commission, Delta Stewardship Council, North Delta Water Agency, Central Delta Water Agency, South Delta Water Agency, Center for Watershed Sciences, and UC Water
Project Documents and Datasets
California Water Blog
Full Authors and Contributors List
Josué Medellín-Azuara1,2, Kyaw Tha Paw U3, Yufang Jin3, and Jay R. Lund1
Report Preparation and Research Assistance
Jesse Jankowski, Eric Kent, Jenae' Clay, Andy Wong, Andrew Bell, Nicholas Santos, and Jessica Badillo, University of California, Davis
Other collaborators and research support from:
Commissioned by the Office of the Delta Watermaster
Michael George, Delta Watermaster, California State Water Resources Control Board
Field Campaign Group
Kyaw Tha Paw U3, Eric Kent3, Jenae’ Clay3, Michelle Leinfelder-Miles4, Jean-Jacques Lambert3, Megan McAuliffe3, David Edgar3, Sean Freiberg3, Ruolan Gong3, Megan Metz3, Cayle Little5, Bekele Temegsen5
CalSIMETAW: Morteza Orang5, Richard L. Snyder3,4, Quinn Hart1,3, Sara Sarreshteh5, and Simon Eching5
DETAW: Tariq Kadir5 and Lan Liang5
DisALEXI: Martha Anderson6
ITRC: Daniel Howes6
SIMS: Forest Melton8,9, Alberto Guzmán8,9, Lee Johnson8,9, Carolyn Rosevelt8,9, and Kirk Post8,9
UCD-METRIC: Nadya Alexander1, Nicholas Santos3, Andrew Bell1, Justin Merz1 and Quinn Hart1,3
UCD-PT: Yufang Jin3, Andy Wong3
Unmanned Aerial Vehicles: J. Andrés Morandé1, Ricardo Trezza5, Andreas Anderson2, Kyaw Tha Paw U3, Yufang Jin3, Josué Medellín-Azuara1,2, Jesse Jankowski1, Jessica Badillo1, Joshua H. Viers2, YangQuan Chen2
WRF-ACASA: Kyaw Tha Paw U3, Eric Kent3, Jenae’ Clay3, Rex David Pyles3
Peer Review Panel
Richard Allen10, Byron Clark11, Richard L. Snyder3,4 and Thomas Trout6
1 Center for Watershed Sciences, University of California, Davis
2 School of Engineering, University of California, Merced
3 Land, Air and Water Resources, University of California, Davis
4 University of California Cooperative Extension.
5 California Department of Water Resources
6 Agricultural Research Service, United States Department of Agriculture
7 Irrigation Training and Research Center, California Polytechnic State University, San Luis Obispo
8 NASA-Ames Research Center, Cooperative for Research in Earth Science and Technology
9 California State University, Monterey Bay
10 University of Idaho, Kimberly
11 Davids Engineering, Inc.